<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><title>Help - Estimation and Subtraction of Topographic Phase, "SRD Operator"</title>

    <link rel="stylesheet" href="../style.css"></head>
<body>
<table class="header">
    <tbody>
    <tr class="header">
        <td class="header">&nbsp; Estimation and Subtraction of Topographic Phase (InSAR operator)</td>
        <td class="header" align="right"><a href="../general/Overview.html"><img src="../images/snap_header.jpg" border="0"></a></td>
    </tr>
    </tbody>
</table>
<h3>Estimation and Subtraction of Topographic Phase</h3>

<p>
    This operator estimates and subtracts topographic phase from the interferogram.
    More specifically, this operator first "radarcodes" the Digital Elevation Model (DEM)
    of the area of interferogram, and then subtracts it from the complex interferogram.
</p>

<p>
    This operator has to be performed after the interferogram generation. It also requires
    an input DEM, SRTM can be used, or any other supported DEM. The DEM handling
    for most of elevation models, selection and download from internet of tiles covering
    the area of interest, interpolation, accounting for geoid undulation, etc, is performed
    automatically by the operator itself.
</p>

<h4>Implementation Details</h4>

<p>The DEM reference phase is computed in two steps:</p>

<ul>
    <li>
        In first step, the DEM is radarcoded to the coordinate systems of the master
        image. Per DEM point the master coordinate (real valued) and the
        computed reference phase is saved to a file.
    </li>
    <li>
        Then, the reference phase is interpolated to the integer grid of master
        coordinates. A linear interpolation based on a Delaunay triangulation is used.
    </li>
</ul>

<h4>Operator parameters:</h4>
<ol>
    <li>
        <b>Orbit Interpolation Degree:</b> Degree of orbit interpolation polynomial.
    </li>
    <li>
        <b>Digital Elevation Model:</b> Elevation model to be used for the processing.
    </li>
    <li>
        <b>Tile Extension [%]:</b> Define extension of tile for DEM simulation (optimization parameter).</li><li><span style="font-weight: bold;">Output topographic phase band:</span> Optional. The subtracted topographic phase.</li><li><span style="font-weight: bold;">Output elevation band:</span>&nbsp;Optional. Interpolated and radarcoded height of the area-of-interest.</li><li><span style="font-weight: bold;">Output orthorectified Lat/Lon bands:</span> Optional. Orthorectified latitudes and longitudes.</li>
</ol>

<h4>Input/Output bands:</h4>

<p> <b>Source Bands</b> are stack of flat-earth subtracted ("flattened") interferograms.</p>

<p> <b>Output Bands</b> are stack of interferograms with subtracted DEM reference phase and other optional bands,
    for example: radarcoded elevation of the area, of topographic phase.
</p>

<h4>Known issues:</h4>&nbsp;&nbsp;
<p>
    When using 'External DEM' as a reference surface, user has to make sure that the input DEM sufficiently covers and
    and extends, the area of input interferogram. In practice, this means that the input DEM should be 10-15%
    bigger in its extent (wider and higher) then the interferogram.
</p>

<br>
<br>
<hr>
</body></html>